What are Keratitis?
Keratitis can be a serious disease, threatening your horse’s vision. It usually only affects one eye, but there have been cases where both eyes are affected, leading to total blindness. In many cases, your equine veterinarian may refer you to a specialized equine ophthalmologist.
Immune-mediated keratitis, IMMK, or commonly called just keratitis, is a non-infectious eye disease. It is quite common in horses and is recognized by a chronic corneal opacity that does not present an ulceration or uveitis.
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Symptoms of Keratitis in Horses
Daily examinations of your horse should be done, including looking at your horse’s eyes for any signs of change. If you notice any changes within your horse’s eyes, contact your veterinarian for an appointment. Your veterinarian may then refer you to a specialist, usually an equine ophthalmologist.
- Inflammation of the eyelids
- Congestion of the blood vessels in the conjunctiva
- Swelling of the conjunctiva
- Water eye
- Corneal edema, eye appears white or bluish
- Ocular discharge
- Excessive amount of blood vessels within the cornea
- Softening of the cornea
- Drying or ulceration of the cornea
- Proliferation of blood vessels within the cornea
- Aversion to light
- Pupil constriction
There are four types of keratitis in horses. The types are based on the clinical signs, effects on the cornea, and response to medical intervention.
There is no underlying stromal edema but within the superficial opacity there will be irregular clumps or lines of thickened epithelium. When a light is shined on the cornea, the cornea will look rough and jagged instead of smooth. It generally occurs where the upper and lower eyelids meet. Epithelial keratitis is the most superficial type; your horse may experience discomfort.
Chronic Superficial Stromal Keratitis
There is prominent subepithelial arborizing vascularity from the limbus. The limbus are the blood vessels that look like tree branches. There is usually an increased blood flow within the eye. You may notice a yellow-white tint to the cornea when light is shined into the cornea.
Chronic Deep Stromal Keratitis
The blood vessels within the eye have ruptured. This causes plasma to be released into the stroma, giving the cornea a green-yellow tint. Your horse will experience significant pain when the blood vessels rupture.
The innermost layer of cells within the cornea, or the endothelium, is affected. When the endothelium is damaged, it stops moving water from the cornea and it starts to turn color. This is the most dangerous and damaging type of keratitis. Endotheliitis can progress into glaucoma. This is very painful for your horse.
Causes of Keratitis in Horses
Researchers believe that keratitis in horses occurs when there is a severe corneal immune response to a microbial antigen, self-antigen or foreign protein. Horses diagnosed with keratitis will be classified into four different types based on the depth of the inflammatory response.
A horse’s eye has the ability to slough off damaged cells when your horse has been sick or injured. This is how the cornea heals. Normally, your horse’s cornea is clear, however, if it is injured the color turns colors.
Diagnosis of Keratitis in Horses
Your veterinarian will perform an ocular examination to diagnose and assess the severity of the keratitis. Your horse will need to be properly restrained and given a light sedative. In some cases a nerve block may also need to be used so a full assessment can be made.
The eye should be stained so any defects within the cornea can be seen. Any abrasions to the cornea can be very hard to see without stains. Any defects in the outer layer of the cornea allow the stain to diffuse into the middle layer. The lesions will appear bright green.
Your veterinarian may not be able to perform an ocular examination. If that is the case, then an equine ophthalmologist specialist will be recommended.
Treatment of Keratitis in Horses
Your veterinarian will set a treatment plan in place that will manage your horse’s keratitis. Most horses that have been diagnosed with keratitis will need the disease managed medically to keep your horse from going blind in the affected eye. Surgery should be a last resort.
Managing keratitis medically will require that your horse be put on a medication regimen. Your horse may be stubborn and refuse to accept their medications. When this happens, your veterinarian may suggest a subpalpebral lavage where a flexible tube is inserted into the upper and lower eyelids and then stitched into place. The medication is administered through the tube. Antibiotic, anti-fungal, anti-inflammatory, atropine and anti-protein medications may be prescribed.
There are five surgical options that may be available for your horse if managing with medications is not proving effective. Deep ulcers or non-responsive ulcers will generally require surgery. Your veterinarian will discuss your surgical options and which surgery will be the best for your horse. There are some extreme cases where complete enucleation will be necessary. This is when the eye must be removed surgically.
Grid Keratotomy is a procedure that involves making grid lines on the surface of the cornea This will allow healthy cells to develop and promote quicker healing.
Ulcer Debridement is a procedure that involves removing the dead tissue around the ulcers edges.
Conjunctival Flap is a procedure that involves the use of a flap of your horse’s conjunctiva to cover the ulcer and promote healing.
Corneal Graft is a procedure that involves using a cornea from a donor horse.
Amniotic Membrane Graft is a procedure that is similar to a corneal graft except fetal membranes are harvested from mares to cover the cornea.
Recovery of Keratitis in Horses
Early detection and treatment are important to saving your horse’s sight. It may become necessary later on to remove the eye or blindness may occur. Long term medical management will be required to keep your horse’s keratitis under control. Always follow the treatment plan that your veterinarian has set to ensure that your horse’s eye health is being maintained. If you notice any changes within the eye, contact your veterinarian immediately to update your horse’s treatment plan.